CS4237B Datasheet, PDF (81/114 Pages) Cirrus Logic – CrystalClear Advanced Audio System with 3D Sound

CS4237B
with the rest of the bits in I22, are used to set the
sample frequency. Once enabled, these bits can
be changed without doing an MCE cycle.
The third method supports independent sample
frequencies (Fs) for capture and playback. The
independent sample frequency mode is enabled
by setting IFSE in X11. Once enabled, the other
two methods for setting Fs (I8, I10, and I22) are
disabled. The capture (ADC) Fs is set in X12
and the playback (DAC) Fs is set in X13.
Changing Audio Data Formats
In MODE 1, MCE must be used to select the
audio data format in I8. Since MCE causes a
calibration cycle, it is not ideal for full-duplex
operation. In MODE 2 and 3, individual Mode
Change Enable bits for capture and playback are
provided in register I16. MCE (R0) must still be
used to select the sample frequency, but PMCE
(playback) and CMCE (capture) allow changing
the respective data formats without causing a
calibration to occur. Setting PMCE (I16) clears
the playback FIFO and allows the upper four
bits of I8 to be changed. Setting CMCE (I16)
clears the capture FIFO and allows the upper
four bits of I28 to be changed.
Audio Data Formats
In MODE 1 operation, all data formats of the
WSS Codec are in "little endian" format. This
format defines the byte ordering of a multibyte
word as having the least significant byte occupy-
ing the lowest memory address. Likewise, the
most significant byte of a little endian word oc-
cupies the highest memory address.
The sample frequency is always selected in the
Fs & Playback Data Format register (I8). In
MODE 1 the same register, I8, determines the
audio data format for both playback and capture;
however, in MODE 2 and 3, I8 only selects the
playback data format and the capture data format
is independently selectable in the Capture Data
Format register (I28).
DS213PP4
The WSS Codec always orders the left channel
data before the right channel. Note that these
definitions apply regardless of the specific for-
mat of the data. For example, 8-bit linear data
streams look exactly like 8-bit companded data
streams. Also, the left sample always comes first
in the data stream regardless of whether the sam-
ple is 16-bit or 8-bit in size.
There are four data formats supported by the
WSS Codec during MODE 1 operation: 16-bit
signed (little endian), 8-bit unsigned, 8-bit com-
panded µ-Law, and 8-bit companded A-Law.
See Figures 14-17.
Additional data formats are supported in MODE
2 and 3: 4-bit ADPCM, and 16-bit signed Big
Endian. See Figures 18 through 21. With the ad-
dition of the Big Endian and ADPCM audio data
formats, the WSS Codec is compliant with the
IMA recommendations for digital audio data for-
mats (and sample frequencies).
16-BIT SIGNED
The 16-bit signed format (also called 16-bit 2’s
complement) is the standard method of repre-
senting 16-bit digital audio. This format gives
96 dB theoretical dynamic range and is the
standard for compact disk audio players. This
format uses the value -32768 (8000h) to repre-
sent maximum negative analog amplitude, 0 for
center scale, and 32767 (7FFFh) to represent
maximum positive analog amplitude.
8-BIT UNSIGNED
The 8-bit unsigned format is commonly used in
the personal computer industry. This format de-
livers a theoretical dynamic range of 48 dB. This
format uses the value 0 (00h) to represent maxi-
mum negative analog amplitude, 128 for center
scale, and 255 (FFh) to represent maximum
positive analog amplitude. The 16-bit signed and
8-bit unsigned transfer functions are shown in
Figure 22.
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